The basic concept of spinning fibers is centuries old. Spinning staple fibers into useful threads and yarns improved their overall strength, to a limited extent, and allowed the final yarn to be spun with varying degrees of thickness, strength, etc.
With the advent of synthetic textile fibers, the possibility arose for producing continuous filament yarns with greater strength and more durability than those from staple fibers, and also no shrinkage. Accordingly, it has become possible to produce knitted and woven fabrics for apparel, home furnishing and industrial use. The shrinkage of these fabrics can be controlled by using a yarn where the heat annealing point of the polyester fiber which is spun into the continuous filament state has been exceeded. Products made from polyester yarn have excellent strength properties, dimensional stability and good color fastness to washing, dry cleaning and light exposure. The use of 100% polyester knit and woven fabrics became extremely popular during the late 1960's and through the 1970's. More recently, continuous filament polyester fiber has also been cut into staple where it can be spun into 100% polyester staple yarns or blended with cotton or other natural fibers. However, both 100% polyester and polyester blended yarns and fabric made from these yarns have a shiny and synthetic appearance, are clammy and prone to static conditions in low humidity, and tend to be hot and sticky in high humidity conditions. Additionally, polyester fiber, because of its high tensile strength, is prone to pilling in staple form and picking in continuous filament form.
Conventional methods of blending cotton and synthetics together have been less than fully successful as both mechanical and intermittent blends of polyester and cotton tend to pill, pick, shrink and are uncomfortable to wear. The consumer's use of polyester and polyester blended fabrics has been reduced over recent years in favor of 100% cotton fabrics which offer good appearance and comfort. This is especially true in the apparel industry. However, the use of 100% cotton yarn and fabrics also has its disadvantages. Primarily, fabrics made of 100% natural cotton tend to shrink and wrinkle. The most popular method of controlling cotton shrinkage for apparel outerwear is to coat the cotton fabric with resins made of formaldehyde. However, formaldehyde is considered to be a hazardous chemical and is therefore dangerous to handle during processing and is also considered dangerous on any fabrics that come into contact with the body because formaldehyde is a known carcinogen. Additionally, formaldehyde-based resins, when used to control the shrinkage of cotton or cotton blend fabrics, degrade the abrasion resistant and strength properties of the fabric, thus making them more prone to fabric holes and scuffing.
The use of prewashing to control shrinkage is also less than satisfactory because it is wasteful in terms of the energy consumed and it also gives garments a worn appearance. Mechanical compaction has also been used to control the shrinkage of cotton fabrics. However, this process is expensive because of the high working loss and it is also not a permanent solution as compacted garments tend to return to their pre-compacted dimensions. For these reasons, the treating of cotton by resin is the currently preferred method to control the shrinkage of cotton fabrics. However, because most resins contain formaldehyde, the fabrics treated with resin are unsafe both during the manufacturing process and during their use by the consumer.
Accordingly, there is a need in the art to produce yarns that have both the positive qualifies of cotton fibers and synthetic filaments while eliminating their respective negative qualities. Composite yarns, per se, have been manufactured for many years. A well-known method of spinning both homogenous and composite yarns has been ring spinning, which has several advantages. For example, ring spinning produces a strong yarn of high quality, with a low capital investment per spindle. Unfortunately, ring spinning is a comparatively slow process, capable of producing only about 10 to 25 meters of yarn per minute, which greatly increases the cost of the final product. Still, since no other previously known process could produce the strength or feel of ring-spun yarn, this process is still used when the demand for its strength and feel justifies the high costs involved.
Other spinning machines and methods have been developed in more recent years in an attempt to produce a composite yarn with the quality of a ring-spun yarn. Some of these methods include open-end, vacuum, and air-jet spinning, which are capable of output capacities exceeding 10 to 25 times that of ring spinning. One such method is disclosed in U.S. Pat. No. 4,069,656 to Arai et al. Arai describes a process for producing yarns at high speed by feeding a bundle of short fibers along with fine multifilament yarn into a twisting device. The filament yarn is fed at sufficiently low tension and at a faster speed than the fibers such that the fine yarn becomes wrapped around the short fibers. Supposedly, the non-twisted configuration of the fiber bundle provides a good feel to the yarn.
However, the alternating twist of the yarn in this patent precludes its use as a sewing thread, where tear-resistance and high uniformity are required. Additionally, thread made from filament yarns such as that disclosed by Arai have smooth outer surfaces, which causes them to be easily pulled from seams. To date, high quality goods have consistently used mainly ring-spun staple fibers for thread, but as mentioned above, this greatly increases the costs.
Another attempt to create a high-quality composite yarn is disclosed in U.S. Pat. No. 4,866,924 to Stahlecker. A fiber component is first formed by a drawn sliver that is pre-strengthened by false twist spinning. A filament yarn is then taken up with the fiber component onto a spool for subsequent spinning, using a conventional spinning method. According to the patent, when high demands are made on the composite yarn, such as are made on ring-spun staple fibers, it is necessary to rewind the yarn and clean it out so that defects, such as thick or thin points, can be removed. Obviously, the cost involved in rewinding the yarn, among other deficiencies, makes this yarn unacceptable as a viable, cost-effective alternative to ring-spun yarn.
U.S. Pat. No. 4,921,756 to Tolbert et al. discloses another attempt to create a high quality composite yarn. Core 11 is made from high temperature resistant continuous filament fiber glass and comprises about 20 to 40% of the total weight of the composite yarn. A sheath 12 of low temperature resistant staple fibers surrounds the core 11 and comprises from about 80 to 60% of the total weight of the composite yarn. A minor portion of the staple fibers 13 may be separated from the sheath 12 to form a binding wrapper spirally wrapped around the majority of the staple fibers. According to this patent, a glass-based core 11 is required to maintain the fire resistant property of the composite yarn.
In U.S. Pat. No. 4,928,464 of Morrison, a core filament yarn is tensioned and dragged over the sharp edge of a nonconductive material. After releasing the tension, a crimp develops on the filaments. The crimped filament yarn is then fed into a vacuum spinning device along with nipped sliver or roving. The crimp of the core filaments causes the individual filaments to repel each other and allows the sliver or roving to become partially intermixed with the core during spinning. When the core filaments enter the spinner, they are only tensioned sufficiently to carry them through the apparatus. In the final product, the fibers, while partially intermixed with the core, are relatively loosely spun around the core, allowing them to slide along it and expose the filament yarn beneath. This degrades the look and feel of any fabric produced with the yarn. This sliding phenomenon is known to occur with many existing composite yarns.
The vacuum spinning disclosed by Morrison is faster than conventional ring spinning, but is still considerably slower than air-jet spinning. In vacuum spinning, a shaft having multiple holes is rotated while suction is applied to the holes. This rotating shaft is capable of a rotational speed much less than that caused by air jets. An effective air-jet spinner is disclosed in U.S. Pat. No. 4,497,167 to Nakahara et al. The dual-nozzle system provides high-speed, uniform spinning. The only necessary tension on the entering fibers is that sufficient to carry the fibers through the nozzles.
The type of air-jet spinner disclosed by Nakahara can also be applied to composite spinners, such as the "High-Speed Type Murata Jet Spinner," manufactured by Murata Machinery, Ltd., Kyoto, Japan. This machine is capable of producing 300 meters per minute, while maintaining uniform spinning. Nevertheless, with any of the known air-jet spinners, it has been impossible to achieve a tight enough wrapping of fibers around a core to prevent any slippage or pilling.